Planar antenna array

ABSTRACT

A circularly polarized planar array of slot antenna elements provide a pencil-beam pattern substantially perpendicular to the plane of the array.

United States Patent 51 3,701,162

Seaton 1 Oct. 24, 1972 [54] PLANAR ANTENNA ARRAY [56] References Cited lnven or 232;; galigeaton, Palos Verdes UNITED STATES PATENTS 73Assignee: Hughes Aircraft p y Culver l DeRosa et al City, calm 2,967,3011/1961 Rearwin "343/771 [22] Filed: March 1964 PrimaryExaminer-Benja.min A. Borchelt [21] Appl. No.: 354,341 AssistantExaminer-Richard E. Berger Attorney-James K. Haskell and Noel B. Hammond[57] ABSTRACT A circularly polarized planar array of slot antennaelements provide a pencil-beam pattern substantially perpendicular tothe plane of the array.

11 Claims, 4 Drawing Figures PATENTEDncI 24 1912 SHEET 1 BF 2 wry/M407/! E $5470,

Amy f PLANAR ANTENNA ARRAY The invention described herein was made inthe performance of work under a NASA contract and is subject of theprovisions of section 305 of the National Aeronautics and Space Act of1958, Public Law 85- 568 (72 Stat. 435; 42 U.S.C. 2457).

Planar arrays are used in applications requiring high gain and highaperture efficiency. However, conventional planar arrays are ordinarilylinearly polarized. Where circular polarization is a requirement, aparabolic antenna, rather than a planar array of slot elements, isusually employed.

However, parabolic antennas have a lower gain and lower apertureefficiency than a planar array and, in addition, are larger and heavier.Hence, attempts have been made to adapt planar arrays to circularpolarizatron.

The so-called leaky pipe waveguide planar array, although usuallylinearly polarized, can be made circularly polarized but it does notprovide a broadside beam, that is, a beam perpendicular to the plane ofthe array. The mode of operation is essentially end-fire, that is, withthe beam substantially parallel to the plane of the array (sometimescalled the zero order beam). The leaky-pipe array cannot be made tooperate in the broadside mode, and tilts the beam at least 40 offbroadside. Aperture efficiency is low because the effective aperture isreduced by the cosine of the beam-tilt angle.

The annular slot waveguide planar array also can be made to providecircular polarization but it suffers from the necessity of spacing theslots a full guide wavelength apart. This results in the generation ofsecondary maxima, that is, in addition to the broadside lobe, the arraygenerates other large lobes at large angles off broadside. Consequently,the annular slot antenna has low efficiency.

Circularly polarized traveling wave linear arrays providing a broadsidebeam have been constructed employing nonresonant crossed slots on thebroad wall of a waveguide operating in the TE mode. These linear arraysmay be combined to form planar arrays but such an array also has anextremely low aperture efficiency because, again, a large slot spacingis required. This large slot spacing is necessitated by the fact thatcrossed slots can be used only on one side of the centerline of thewaveguide for a given sense of circular polarization (i.e., right-handor left-hand circular polarization). Crossed slots on the other side ofthe centerline radiate a circularly polarized wave of the oppositesense. Broadside operation of the array thus requires that the slots bespaced a full guide wavelength apart. This spacing, which isapproximately equal to 1.4 times a free-space wavelength, allows thegeneration of secondary maxima which seriously detract from theprincipal maximum, or main lobe.

Accordingly, it is an object of the present invention to provide acircularly polarized planar antenna array having a narrow beam patternsubstantially perpendicular to the plane of the array and havingsubstantially no secondary lobes.

Another object of the invention is the provision of a circularlypolarized planar antenna array having a high efficiency.

Yet another object of the present invention is to provide an efficientcircularly polarized high-gain antenna which is light in weight andwhich has a thin, flat configuration.

In accordance with these and other objects of the invention, there isprovided a thin rectangular enclosure having one broad surface slottedto form radiating elements and the opposing broad surface corrugated toform a slow-wave structure. The rectangular enclosure forms a widerectangular waveguide operating in a multimode fashion to effectivelyproduce a plurality of virtual waveguide linear arrays extendingside-by-side and operating in the traveling wave mode. Circularpolarization is obtained by using nonresonant crossed slots on one sideof the centerline of each virtual waveguide and pairs of separatednonresonant slots on the other side of the centerline. Each pair ofseparated slots is centered between the crossed slots to obtain thecorrect sense of rotation and phase. Alternate linear arrays aredisplaced by half a guide wavelength to account for the phase reversalof the alternate half cycles of the multimode feed arrangement. Theantenna is excited from feed slots in the bottom of the firstcorrugation trough of each linear array. The feed slots are shunt-typeslots in a feed waveguide extending tranversely across the ends of thelinear arrays. The feed waveguide operates as a standing wave array andis centerfed by means of a magnetic loop coax-towaveguide transition.Conductive strips serving as mode suppressors extend from thecorrugations to the aperture plate along the line of the virtualwaveguide walls.

The following specification and the accompanying drawings describe andillustrate an exemplary embodiment of the present invention.Consideration of the specification and the drawings will provide anunderstanding of the invention, including the novel features and objectsthereof. Like reference characters denote like parts throughout thefigures of the drawings.

FIG. 1 is a plan view of an embodiment of a planar antenna array inaccordance with the invention, with a portion of the aperture platebroken away to show the interior;

FIG. 2 is a perspective view, partly broken away, of a portion of theplanar array of FIG. 1;

FIG. 3 is a schematic diagram indicating the current distribution in aportion of the planar array of FIGS. 1 and 2; and

FIG. 4 is a vector diagram indicating the relative exciting voltages forthree different instants of time of the slots shown in schematic diagramof FIG. 4.

Circularly polarized arrays can be constructed by using crossed slots onthe broadwall of a waveguide at a point of circular polarization of themagnetic fields within the waveguide. However, efficient apertureillumination is difficult to obtain using these slots along since theymust be spaced a full guide wavelength apart in order to keep theradiated fields in phase. This results in a free space distance betweenelements of approximately 1.4 multiplied by a free space wavelength.This large spacing is undesirable because it results in a loss ofaperture efficiency in the generation of secondary maxima (also known assecond order beams or grating lobes).

In a linearly polarized broadwall shunt slot array it is conventional toplace consecutive slots at a half guide wavelength spacing but onopposite sides of the centerline, thereby keeping all slots in phase.This technique will not work with crossed slots because only thetransverse components of current on the waveguide walls are reversed onthe opposite side of the centerline. The longitudinal components are inphase at all points across the guide at any given transverse plane. Thissituation results in circular polarization of the opposite sense beingradiated from crossed slots placed on the opposite side of the guide.

To solve these problems, the present invention employs additional slotsin a new arrangement which together with a slow wave structure produceadequate interelement spacings. These additional slots are also of thenonresonant type, and may be considered to be the two orthogonalportions of a crossed slot separated by a spacing of half a guidewavelength. The separated slots are located on the waveguide relative tothe position of the normal crossed slot such that at broadside both thenormal crossed slot and the separated crossed slot radiate a circularlypolarized wave in phase and of the same sense.

In FIG. 1 there is illustrated an exemplary embodiment of a circularlypolarized planar array constructed in accordance with the presentinvention. There is provided a thin, rectangular enclosure 11 made ofmetal or other conductive material. The rectangular enclosure 11 forms awide rectangular waveguide suitable for excitation in a multimodemanner. In the present example, the enclosure 11 is 38.5 inches squareand 1 inch thick. One broad surface 12 of the enclosure 11 is slotted toform radiating elements. The other broad surface 13 of the enclosure 11is corrugated to form a slow-wave structure.

When the enclosure 11 is excited, it operates as a plurality ofrectangular waveguide linear arrays extending side-by-side. In thepresent example, none virtual waveguides are formed. No waveguide wallsare necessary to separate the virtual waveguides because theelectromagnetic fields operate as if there were solid walls between thevirtual waveguides. However, due to the lack of mirror image symmetry inthe slots on each side of the virtual walls, mode suppressors 14 areemployed. The mode suppressors 14 are elongated metal strips extendingalong the virtual walls between the aperture surface 12 and the crest ofthe corrugated surface 13, and form partial waveguide walls. The modesuppressors l4 suppress undesirable propagation modes in the virtualwaveguides.

The first virtual waveguide is indicated by the bracket 15 extendingacross the broad dimension thereof at the feed end. On one side of thewaveguide centerline, there is a row of crossed-slot elements 16. Eachcrossed-slot element 16 is formed of two intersecting orthogonal slots17, 18. The slots 17, 18 are disposed at an angle of 45 with respect tothe sides of the enclosure 11 so that they can be elongated withoutextending past the waveguide edge. The crossed-slot elements 16 arelocated at the point in the waveguide where the wall currents arecircularly polarized and are spaced approximately one guide wavelengthapart. Actually, the spacing is somewhat less than one wavelength, aswill be discussed hereinafter.

On the other side of the waveguide centerline, there is a row ofseparated slot-pair elements 20. Each separated slot-pair element 20 isformed of two nonintersecting orthogonal slots 17', 18'. These slots17', 18 are also oriented at an angle of 45 with respect to the sides ofthe enclosure 11, and at an angle of with respect to each other. Eachslot designated 17' of a separated slot-pair element 20 is parallel to aslot designated 17 of a crossed-slot element 16. Similarly, each slotdesignated 18' of a separated slot-pair element 20 is parallel to a slotdesignated 18 of a crossedslot element 16. The centers of the two slots17 18' of each separated slot-pair element 20 are spaced nominally halfa guide wavelength apart, as modified by spacing factors to bediscussed. Each separated slotpair element 20 is centered longitudinallyalong the guide between two crossed-slot elements 16. With this slotpattern, the crossed-slot elements 16 and the separated slot-pairelements 20 radiate a circularlypolarized wave in-phase and of the samesense.

The slot pattern for each of the other waveguides is the same exceptthat the slot pattern is displaced by half a guide wavelength inalternate waveguides to account for the phase reversal of the alternatehalf cycles of the multimode excitation. The planar array 10 may beconsidered to be nine linear arrays, each having slotpair elements 16,20 staggered across the centerline to obtain in-phase, circularlypolarized radiation from an interelement spacing of half a guidewavelength.

FIG. 3 schematically shows the currents for the TE mode on the broadwallof a slotted rectangular waveguide representing one of the slottedvirtual waveguides of the planar array 10 of FIGS. 1 and 2. By notingthe direction of the current lines exciting the crossed slots 17, 18 asthe wave progresses down the waveguide, it can be determined that theradiated field is left-hand circularly polarized for a wave coming outof the page. The field is circularly polarized rather than ellipticallypolarized because the slots 17, 18 are displaced laterally from thecenterline to the location where the magnitude of the current remainsconstant as the wave propagates or, in other words, where the magnitudesof the longitudinal and transverse currents (which are 90 in time-phase)are equal.

The separated slots 17', 18' are disposed on the opposite side of thecenterline and centered between the crossed slots 17, 18 to provide thecorrect sense of rotation and phase with respect to that of the crossedslots 17, 18. The lateral displacement of the separated slots 17, 18from the centerline is identical to that of the crossed slots 17, 18,because the same criterion holds. FIG. 4 vectorially illustrates therelative exciting voltages in the slots 17, 17, 18, 18' at threesuccessive instants of time differing from each other by 45 in phase ofthe wave traveling in the direction of propagation shown in FIG. 3. Thesummation of the vectors, indicated as E, in FIG. 4, represents theaddition that takes place in the direction of the main beam. As may beseen from FIG. 4, the total electric field propagated in the directionof the main beam from the two separated slots 17, 18 is always equal inamplitude, orientation and phase to the electric field propagated inthat direction from the crossed slots 17, 18.

The planar array 10 may also be considered to be two interlaced linearlypolarized planar arrays orthogonal to each other and fed in timequadrature. That is, all of the slots oriented in the direction of slotsl7 and 17' may be viewed as one linear array arranged in rows of slots,with the slots closely spaced more or less end-to-end, and the rowswidely spaced. The rows extend at an angle to the sides of the enclosure1 1 along lines through the centers of the slots, such as the row ofslots indicated by the line in the direction of the arrows 19-19 shownin FIG. 1. Similarly, all of the slots oriented in the direction ofslots 18 and 18 may be viewed as rows of slots forming the secondlinearly polarized array orthogonal to the first.

To adequately suppress secondary maxima (second order beams or lobes) inorder to obtain high aperture efficiencies, the interrow spacing hasbeen reduced to less than a free-space wavelength. This is accomplishedby means of the corrugated surface 13 which forms a slow-wave structurethat provides a 25 percent reduction in guide wavelength. When the array10 is considered as two interlaced linearly polarized planar arrays, itis apparent that the separation between slots in the same row, such asthe row indicated by the arrows 19-19 in FIG. 1, is much less than afree-space wavelength. By use of the corrugated surface 13 as aslow-wave structure, the orthogonal separation between rows is reducedto 0.8 of a free-space wavelength. In this manner, anaperture-efficiency of 92 percent was obtained.

To obtain maximum gain, the planar array 10 is uniformly illuminated.Accordingly, because this is a traveling wave array and not a standingwave array, the coupling coefficient of each succeeding slot 17, 17',18, 18 is made progressively larger as the distance down each virtualwaveguide from the feed point becomes larger. The coupling coefficientis increased by increasing the length of the slots which makes them morenearly resonant. In this manner, each pair of slots radiates the sameamount of power. The last slot is adjusted to couple out as much of theremaining power as possible. To compensate for phase differences thusintroduced, the spacing between the slots is gradually decreased as thedistance from the feed point becomes larger. The end of the enclosure 11farthest from the feed end is closed or shorted in the present example,although it may also be left open if desired.

To obtain a predetermined space coverage and good impedance match, thebeam is tilted 6 back towards the feed end by decreasing the slotspacing an additional amount. The result of this reduction of slotspacing is to reduce the row spacing by some fraction of the percentageof reduction in slot spacing. This reduction in slot spacing is alsohighly desireable from the standpoint of input impedance. A separationof one guide wavelength between the crossed-slot elements 16 results ina separation of a half guide wavelength between the separated slots 17',18'. The disadvantage of exactly halfa guide wavelength spacing is thatreflections from the slots would all add in-phase, thereby producing ahigh voltage-standing-wave-ratio at the input to the linear arrays.

The linear arrays are fed from a rectangular feed waveguide 25 (bestseen in FIG. 2) operating as a standing wave array and locatedunderneath the radiation virtual waveguides and at one end of the array10. Coupling from the feed waveguide 25 to the linear arrays isaccomplished by nonresonant longitudinal shunt slots 26 located in thebroad wall of the feed waveguide 25 and opening into the first trough inthe corrugated surface 13. The coupling or feed slots 26 are spacedapart by half a free space wavelength and are disposed on the same sideof the centerline of the feed waveguide 25 to provide 180 phase shiftbetween each of the feed slots 26. The feed waveguide 25 is terminatedin shortcircuits at each end, one-quarter guide wavelength beyond thelast feed slots 26. The reactive component of the admittance is tunedout at each feed slot 26 by an inductive post 27 disposed at each feedslot 26. A coaxial connector 28 couples to the feed waveguide 25 bymeans of a coupling loop 30 located opposite the central feed slot 26.

For operation at a frequency of 2,295 megacycles per second, the broaddimension of each virtual waveguide is 4.267 inches and the narrowdimension is 0.991 inch. The corrugated surface 13 has a dimension of0.491 inch from the crests to the troughs, and the corrugations are 0.1inch in width and are separated by 0.4 inch. By constructing the array10 of thin aluminum (on the order of from 0.003 0.010 inch thick, forexample), the total weight of the array 10 is very small, 8% pounds forexample.

An embodiment of an array constructed in accordance with the presentinvention provided an over all efiiciency of percent, apertureillumination efficiency of 92 percent and a gain of 27.0 decibels. Themeasured ellipticity of the polarization was 1.0 decibel.

Thus, there has been described an efficient, circularly polarized planarantenna array providing a pencilbeam pattern substantially perpendicularto the plane of the array by virtue of employing crossed slots andseparated slots in a new arrangement, in conjunction with a slow-wavestructure.

While only one embodiment of the invention has been shown and described,variations may be made, and it is intended that the foregoing disclosureshall be considered only as illustrative of the principles of theinvention and not construed in a limiting sense.

What is claimed is:

1. A circularly polarized antenna array comprising:

a. means defining at least one waveguide having a broad wall, saidwaveguide being capable of supporting a traveling wave TE mode ofpropagation when excited;

. said waveguide including means defining a slowwave structure providinga reduction in guide wavelength;

. said broad wall having at least two pairs of crossed slots orthogonalto each other, said pairs of crossed slots being longitudinallyseparated from each other by substantially one guide wavelength, saidcrossed slots being disposed laterally on one side of the centerline atthe locations at which the wall currents are circularly polarized whensaid waveguide is excited;

. and said broad wall having at least two nonintersecting slotsorthogonal to each other, said nonintersecting slots beinglongitudinally separated from each other by substantially half a guidewavelength, said nonintersecting slots being disposed laterally on theother side of said centerline from said crossed slots and beingpositioned in relation to said crossed slots such that radiation fromsaid nonintersecting slots is in phase with radiation from said crossedslots.

2. A circularly polarized antenna array comprising:

a. means defining at least one waveguide having a broad wall, saidwaveguide being capable of supporting a traveling wave TE mode ofpropagation when excited;

b. said waveguide including means defining a slowwave structureproviding a reduction in guide wavelength;

c. said broad wall having at least two pairs of crossed slots orthogonalto each other and at an angle of substantially 45 to the longitudinalcenterline of said waveguide, said pairs of crossed slots beinglongitudinally separated from each other by substantially one guidewavelength, said crossed slots being disposed laterally on one side ofsaid centerline at the locations at which the wall currents arecircularly polarized when said waveguide is excited;

d. and said broad wall having at least two nonintersecting slotsorthogonal to each other and at an angle of substantially 45 to thelongitudinal centerline of said waveguide, said nonintersecting slotsbeing longitudinally separated from each other by substantially half aguide wavelength, said nonintersecting slots being disposed laterally onthe other side of said centerline from said crossed slots and beingcentered longitudinally between said crossed slots, the ends of saidnonintersecting slots that are proximate to said centerline beingfarther apart than the other ends thereof.

3. A circularly polarized linear antenna array comprising:

a. a rectangular waveguide having first and second opposing broad walls,said waveguide being capable of supporting a traveling wave TE mode ofpropagation when excited;

b. said first broad wall being corrugated to define a slow-wavestructure providing 25 percent reduction in guide wavelength;

c. said second broad wall having two pairs of crossed nonresonant slotsorthogonal to each other and at an angle or 45 to the longitudinalcenterline of said waveguide, said pairs of crossed slots beinglongitudinally separated from each other by substantially one guidewavelength, said crossed slots being disposed laterally on one side ofsaid centerline at the locations at which the wall currents arecircularly polarized when said waveguide is excited;

d. and said second broad wall having two nonintersecting nonresonantslots orthogonal to each other and at an angle of 45 to the longitudinalcenterline of said waveguide, said nonintersecting slots beinglongitudinally separated from each other by substantially half a guidewavelength, said nonintersecting slots being disposed laterally on theother side of said centerline from said crossed slots and being centeredlongitudinally between said crossed slots, the ends of saidnonintersecting slots that are farthest apart being closest to saidcenterline.

4. A circularly polarized linear antenna array comprising:

a. a rectangular waveguide having first and second opposing broad walls,said waveguide being capable of supporting a traveling wave TE modepropagation when excited;

b. said first broad wall being corrugated to define a slow-wavestructure providing substantially 25 percent reduction in guidewavelength;

. said second broad wall having a plurality of pairs d. and said secondbroad wall having a plurality of pairs of nonintersecting nonresonantslots, the two slots of each of said pairs of nonintersecting slotsbeing orthogonal to each other and at an angle of 45 to the longitudinalcenterline of said waveguide, the centers of the two slots of each ofsaid pairs of nonintersecting slots being longitudinally separated fromeach other by substantially half a guide wavelength, saidnonintersecting slots being disposed laterally on the opposite side ofsaid centerline from said intersecting slots, each pair of saidnonintersecting slots being centered longitudinally between pairs ofcrossed slots, the ends of the two slots of each of said pairs ofnonintersecting slots that are proximate to said centerline beingfarther apart than the ends that are distant therefrom.

. A circularly polarized antenna array comprising: means defining atleast one rectangular waveguide having a broad wall, said waveguidebeing capable of supporting a traveling wave TE mode of propagation whenexcited;

. said waveguide including means defining a slowwave structure providinga reduction in guide wavelength;

. said broad wall having a plurality of pairs of interand said broadwall having a plurality of pairs of nonintersecting slots, the two slotsof each of said pairs of nonintersecting slots being orthogonal to eachother and at an angle of 45 to the longitudinal centerline of saidwaveguide, the centers of the two slots of each of said pairs ofnonintersecting slots being longitudinally separated from each other bysubstantially half a guide wavelength, said nonintersecting slots beingdisposed laterally on the opposite side of said centerline from saidintersecting slots, each pair of said nonintersecting slots beingcentered longitudinally between pairs of intersecting slots, the ends ofthe two slots of each of said pairs of nonintersecting slots that areproximate to said centerline being farther apart than the ends that aredistant therefrom.

6. A circularly polarized antenna array comprising: a. means defining atleast one pair of rectangular waveguides each having a broad wall, saidwaveguides being parallel and adjacent and each being capable ofsupporting a traveling wave TE mode of propagation when excited;

b. means coupled to said waveguides for feeding said waveguides 180 outof phase;

c. said waveguides including means defining slowwave structure providinga reduction in guide wavelength;

(1. each of said broad walls having a plurality of pairs of intersectingslots, the two slots of each of said pairs of intersecting slots beingsubstantially orthogonal to each other and at an angle of substantially45 to the longitudinal centerline of said waveguides, the centers ofsaid pairs of intersecting slots being longitudinally separated fromeach other by substantially one guide wavelength, said intersectingslots being disposed laterally on one side of said centerline at thelocations at which the Wall currents are circularly polarized when saidwaveguides are excited;

e. each of said broad walls having a plurality of pairs ofnonintersecting slots, the two slots of each of said pairs ofnonintersecting slots being orthogonal to each other and at an angle of45 to the longituf. and the slot pattern of one of said waveguides beinglongitudinally displaced substantially half a guide wavelength withrespect to the slot pattern of the other of said waveguides.

7. A circularly polarized planar antenna array comprising:

a. a pair of rectangular waveguides each having first and secondopposing broad walls, said waveguides being parallel and adjacent andeach being capable of supporting a traveling wave TE mode of propagationwhen excited;

b. means coupled to said waveguides for feeding said waveguides 180 outof phase;

c. each of said first broad walls being corrugated to define slow-wavestructure providing substantially 25 percent reduction in guidewavelength;

d. each of said second broad walls having a plurality of pairs ofintersecting nonresonant slots, the two slots of each of said pairs ofintersecting slots being substantially orthogonal to each other and atan angle of substantially 45 to the longitudinal centerline of saidwaveguides, the centers of said pairs of intersecting slots beinglongitudinally separated from each other by substantially one guidewavelength, said intersecting slots being disposed laterally one oneside of said centerline at the locations at which the wall currents arecircularly polarized when said waveguides are excited;

e. each of said second broad walls having a plurality of pairs ofnonintersecting nonresonant slots, the two slots of each of said pairsof nonintersecting slots being orthogonal to each other and at an angleof 45 to the longitudinal centerline of said waveguides, the centers ofthe two slots of each of said pairs of nonintersecting slots beinglongitudinally separated from each other by substantially half a guidewavelength, said nonintersecting slots being disposed laterally on theopposite side of said centerline from said intersecting slots, each pairof said nonintersecting slots being centered longitudinally betweenpairs of intersecting slots, the ends of the two slots of each of saidpairs of nonintersecting slots that are proximate to said centerlinebeing farther apart than the ends that are distant therefrom;

f. and the slot pattern of one of said waveguides being longitudinallydisplaced substantially half a guide wavelength with respect to the slotpattern prising:

a. a plurality of rectangular waveguides each having first and secondopposing broad walls, said waveguides being parallel and adjacent andeach being capable of supporting a traveling wave TE mode of propagationwhen excited;

b. means coupled to said waveguides for feeding said waveguides withalternate ones thereof out of phase;

c. each of said first broad walls being corrugated to define slow-wavestructure providing substantially 25 percent reduction in guidewavelength;

(1. each of said second broad walls having a plurality of pairs ofintersecting nonresonant slots, the two slots of each of said pairs ofintersecting slots being substantially orthogonal to each other and atan angle of substantially 45 to the longitudinal centerline of saidwaveguides, the centers of said pairsof intersecting slots beinglongitudinally separated from each other by substantially one guidewavelength, said intersecting slots being disposed laterally on one sideof said centerline at the locations at which the wall currents arecircularly polarized when said waveguides are excited;

e. each of said second broad walls having a plurality of pairs ofnonintersecting nonresonant slots, the two slots of each of said pairsof nonintersecting slots being orthogonal to each other and at an angleof 45 to the longitudinal centerline of said waveguides, the centers ofthe two slots of each of said pairs of nonintersecting slots beinglongitudinally separated from each other by substantially half a guidewavelength, said nonintersecting slots being disposed laterally on theopposite side of said centerline from said intersecting slots, each pairof said nonintersecting slots being centered longitudinally betweenpairs of intersecting slots, the ends of the two slots of each of saidpairs of nonintersecting slots that are proximate to said i llcenterline being farther apart than the ends that are distant therefrom;

f. and the slot pattern of alternate ones of said waveguides beinglongitudinally displaced substantially half a guide wavelength withrespect to the slot pattern of the other of said waveguides.

9. A circularly polarized antenna array comprising: a. means defining awaveguide having first and b. means coupled to said waveguide forfeeding said waveguide with waves which are 180 out of phase alongalternate ones of said axes;

c. said first broad wall being corrugated to define slow-wave structureproviding substantially 25 percent reduction in guide wavelength;

d. said second broad wall having a plurality of pairs of intersectingnonresonant slots and nonintersecting nonresonant slots disposed inlongitudinal rows on alternate sides of each of said axes, the two slotsof each of said pairs of intersecting slots being substantiallyorthogonal to each other and at an angle of substantially 45 to saidaxes, the centers of said pairs of intersecting slots beinglongitudinally separated from each other by substantially one guidewavelength, said intersecting slots being disposed laterally from saidaxes at the locations at which the wall currents are circularlypolarized when said waveguide is excited;

e. the two slots of each of said pairs of nonintersecting slots beingorthogonal to each other and at an angle of substantially 45 to saidaxes, the centers of the two slots of each of said pairs ofnonintersecting slots being longitudinally separated from each other bysubstantially half a guide wavelength, said nonintersecting slots beingdisposed laterally from said axes the same distance as said intersectingslots, each pair of said nonintersecting slots being centeredlongitudinally between pairs of intersecting slots, the ends of the twoslots of each of said pairs of nonintersecting slots that are proximateto one of said axes being farther apart than the ends that are distanttherefrom;

f. and the slot pattern along alternate ones of said axes beinglongitudinally displaced substantially half a guide wavelength withrespect to the slot pattern along the other of said axes.

10. A circularly polarized antenna array comprising:

a. means defining a waveguide having a broad wall,

said waveguide being capable of supporting a plurality of traveling waveTE modes of propagation along parallel longitudinal axes when excited;

b. means coupled to said waveguide for feeding said waveguide with waveswhich are 180 out of phase along alternate ones of said axes;

c. said waveguide including means defining slowwave structure providinga reduction in guide wavelength;

d. said broad wall having a plurality of nonresonant slots arranged inlongitudinal rows parallel to said axes, a row of intersecting pairs ofslots being on one side of each of said axes and a row ofnonintersecting pairs of slots being on the other side of each of saidaxes, the two slots of each of said pairs of slots being substantiallyorthogonal to each other and at an angle of substantially 45 to saidaxes, the centers of said pairs of intersecting slots beinglongitudinally separated from each other by substantially one guidewavelength, said intersecting slots being disposed laterally from saidaxes at the locations at which the wall currents are circularlypolarized when said waveguide is excited, the centers of the two slotsof each of said pairs of nonintersecting slots being longitudinallyseparated from each other by substantially half a guide wavelength, saidnonintersecting slots being disposed laterally from said axes the samedistance as said intersecting slots, each pair of said nonintersectingslots being centered longitudinally between pairs of intersecting slotson the opposite side of the proximate one of said axes, the ends of thetwo slots of each of said pairs of nonintersecting slots that areproximate to one of said axes being farther apart than the ends that aredistant therefrom;

e. and the slot pattern along alternate ones of said axes beinglongitudinally displaced substantially half a guide wavelength withrespect to the slot pattern along the other of said axes.

1 1. A circularly polarized antenna array comprising:

a. means defining a waveguide having a broad wall,

said waveguide being capable of supporting a plurality of traveling waveTE modes of propagation along parallel longitudinal axes when excited;

b. a plurality of mode suppressors disposed in said waveguide forsuppressing modes of propagation other than said plurality of TE modes;

c. means coupled to said waveguide for feeding said waveguide with waveswhich are out of phase along alternate ones of said axes;

d. said waveguide including means defining slowwave structure providinga reduction in guide wavelength;

e. said broad wall having a plurality of nonresonant slots arranged inpairs staggered across said axes at substantially half a guidewavelength spacing intersecting pairs of slots being on one side of eachof said axes and nonintersecting pairs of slots being on the other sideof each of said axes, the two slots of each of said pairs of slots beingsubstantially orthogonal to each other and at an angle of substantially45 to said axes, the centers of said pairs of intersecting slots beinglongitudinally separated from each other by substantially one guidewavelength, said intersecting slots being disposed laterally from saidaxes at the locations at which the wall currents are circularlypolarized when said waveguide is excited, the centers of the two slotsof each of said pairs of nonintersecting s slots being longitudinallyseparated from each other by substantially half a guide wavelength, saidnonintersecting slots being disposed laterally from said axes the samedistance as said intersecting slots, each pair of said nonintersectingslots being centered longitudinally between pairs of intersecting slotson the opposite side of the proximate one of said axes, the ends of thetwo slots of each of said pairs of nonintersecting slots that areproximate to one of said axes being farther apart than the ends that aredistant therefrom; f. and the slot pattern along alternate ones of saidaxes being longitudinally displaced substantially 5 half a guidewavelength with respect to the slot pattern along the other of saidaxes.

1. A circularly polarized antenna array comprising: a. means defining atleast one waveguide having a broad wall, said waveguide being capable ofsupporting a traveling wave TE10 mode of propagation when excited; b.said waveguide including means defining a slow-wave structure providinga reduction in guide wavelength; c. said broad wall having at least twopairs of crossed slots orthogonal to each other, said pairs of crossedslots being longitudinally separated from each other by substantiallyone guide wavelength, said crossed slots being disposed laterally on oneside of the centerline at the locations at which the wall currents arecircularly polarized when said waveguide is excited; d. and said broadwall having at least two nonintersecting slots orthogonal to each other,said nonintersecting slots being longitudinally separated from eachother by substantially half a guide wavelength, said nonintersectingslots being disposed laterally on the other side of said centerline fromsaid crossed slots and being positioned in relation to said crossedslots such that radiation from said nonintersecting slots is in phasewith radiation from said crossed slots.
 2. A circularly polarizedantenna array comprising: a. means defining at least one waveguidehaving a broad wall, said waveguide being capable of supporting atraveling wave TE10 mode of propagation when excited; b. said waveguideincluding means defining a slow-wave structure providing a reduction inguide wavelength; c. said broad wall having at least two pairs ofcrossed slots orthogonal to each other and at an angle of substantially45* to the longitudinal centerline of said waveguide, said pairs ofcrossed slots being longitudinally separated from each other bysubstantially one guide wavelength, said crossed slots being disposedlaterally on one side of said centerline at the locations at which thewall currents are circularly polarized when said waveguide is excited;d. and said broad wall having at least two nonintersecting slotsorthogonal to each other and at an angle of substantially 45* to thelongitudinal centerline of said waveguide, said nonintersecting slotsbeing longitudinally separated from each other by substantially half aguide wavelength, said nonintersecting slots being disposed laterally onthe other side of said centerline from said crossed slots and beingcentered longitudinally between said crossed slots, the ends of saidnonintersecting slots that are proximate to said centerline beingfarther apart than the other ends thereof.
 3. A circularly polarizedlinear antenna array comprising: a. a rectangular waveguide having firstand second opposing broad walls, said waveguide being capable ofsupporting a traveling wave TE10 mode of propagation when excited; b.said first broad wall being corrugated to define a slow-wave structureproviding 25 percent reduction in guide wavelength; c. said second broadwall having two pairs of crossed nonresonant slots orthogonal to eachother and at an angle or 45* to the longitudinal centerline of saidwaveguide, said pairs of crossed slots being longitudinally separatedfrom each other by substantially one guide wavelength, said crossedslots being disposed laterally on one side of said centerline at thelocations at which the wall currents are circularly polarized when saidwaveguide is excited; d. and said second broad wall having twononintersecting nonresonant slots orthogonal to each other and at anangle of 45* to the longitudinal centerline of said waveguide, saidnonintersecting slots being longitudinally separated from each other bysubstantially half a guide wavelength, said nonintersecting slots beingdisposed laterally on the other side of said centerline from saidcrossed slots and being centered longitudinally between said crossedslots, the ends of said nonintersecting slots that are farthest apartbeing closest to said centerline.
 4. A circularly polarized linearantenna array comprising: a. a rectangular Waveguide having first andsecond opposing broad walls, said waveguide being capable of supportinga traveling wave TE10 mode propagation when excited; b. said first broadwall being corrugated to define a slow-wave structure providingsubstantially 25 percent reduction in guide wavelength; c. said secondbroad wall having a plurality of pairs of intersecting nonresonantslots, the two slots of each of said pairs of intersecting slots beingsubstantially orthogonal to each other and at an angle of substantially45* to the longitudinal centerline of said waveguide, the centers ofsaid pairs of intersecting slots being longitudinally separated fromeach other by substantially one guide wavelength, said intersectingslots being disposed laterally on one side of said centerline at thelocations at which the wall currents are circularly polarized when saidwaveguide is excited; d. and said second broad wall having a pluralityof pairs of nonintersecting nonresonant slots, the two slots of each ofsaid pairs of nonintersecting slots being orthogonal to each other andat an angle of 45* to the longitudinal centerline of said waveguide, thecenters of the two slots of each of said pairs of nonintersecting slotsbeing longitudinally separated from each other by substantially half aguide wavelength, said nonintersecting slots being disposed laterally onthe opposite side of said centerline from said intersecting slots, eachpair of said nonintersecting slots being centered longitudinally betweenpairs of crossed slots, the ends of the two slots of each of said pairsof nonintersecting slots that are proximate to said centerline beingfarther apart than the ends that are distant therefrom.
 5. A circularlypolarized antenna array comprising: a. means defining at least onerectangular waveguide having a broad wall, said waveguide being capableof supporting a traveling wave TE10 mode of propagation when excited; b.said waveguide including means defining a slow-wave structure providinga reduction in guide wavelength; c. said broad wall having a pluralityof pairs of intersecting slots, the two slots of each of said pairs ofintersecting slots being substantially orthogonal to each other and atan angle of substantially 45* to the longitudinal centerline of saidwaveguide, the centers of said pairs of intersecting slots beinglongitudinally separated from each other by substantially one guidewavelength, said intersecting slots being disposed laterally on one sideof said centerline at the locations at which the wall currents arecircularly polarized when said waveguide is excited; d. and said broadwall having a plurality of pairs of nonintersecting slots, the two slotsof each of said pairs of nonintersecting slots being orthogonal to eachother and at an angle of 45* to the longitudinal centerline of saidwaveguide, the centers of the two slots of each of said pairs ofnonintersecting slots being longitudinally separated from each other bysubstantially half a guide wavelength, said nonintersecting slots beingdisposed laterally on the opposite side of said centerline from saidintersecting slots, each pair of said nonintersecting slots beingcentered longitudinally between pairs of intersecting slots, the ends ofthe two slots of each of said pairs of nonintersecting slots that areproximate to said centerline being farther apart than the ends that aredistant therefrom.
 6. A circularly polarized antenna array comprising:a. means defining at least one pair of rectangular waveguides eachhaving a broad wall, said waveguides being parallel and adjacent andeach being capable of supporting a traveling wave TE10 mode ofpropagation when excited; b. means coupled to said waveguides forfeeding said waveguides 180* out of phase; c. said waveguides includingmeans defining slow-wave structure providing a reduction in guidewavelength; D. each of said broad walls having a plurality of pairs ofintersecting slots, the two slots of each of said pairs of intersectingslots being substantially orthogonal to each other and at an angle ofsubstantially 45* to the longitudinal centerline of said waveguides, thecenters of said pairs of intersecting slots being longitudinallyseparated from each other by substantially one guide wavelength, saidintersecting slots being disposed laterally on one side of saidcenterline at the locations at which the wall currents are circularlypolarized when said waveguides are excited; e. each of said broad wallshaving a plurality of pairs of nonintersecting slots, the two slots ofeach of said pairs of nonintersecting slots being orthogonal to eachother and at an angle of 45* to the longitudinal centerline of saidwaveguides, the centers of the two slots of each of said pairs ofnonintersecting slots being longitudinally separated from each other bysubstantially half a guide wavelength, said nonintersecting slots beingdisposed laterally on the opposite side of said centerline from saidintersecting slots, each pair of said nonintersecting slots beingcentered longitudinally between pairs of intersecting slots, the ends ofthe two slots of each of said pairs of nonintersecting slots that areproximate to said centerline being farther apart than the ends that aredistant therefrom; f. and the slot pattern of one of said waveguidesbeing longitudinally displaced substantially half a guide wavelengthwith respect to the slot pattern of the other of said waveguides.
 7. Acircularly polarized planar antenna array comprising: a. a pair ofrectangular waveguides each having first and second opposing broadwalls, said waveguides being parallel and adjacent and each beingcapable of supporting a traveling wave TE10 mode of propagation whenexcited; b. means coupled to said waveguides for feeding said waveguides180* out of phase; c. each of said first broad walls being corrugated todefine slow-wave structure providing substantially 25 percent reductionin guide wavelength; d. each of said second broad walls having aplurality of pairs of intersecting nonresonant slots, the two slots ofeach of said pairs of intersecting slots being substantially orthogonalto each other and at an angle of substantially 45* to the longitudinalcenterline of said waveguides, the centers of said pairs of intersectingslots being longitudinally separated from each other by substantiallyone guide wavelength, said intersecting slots being disposed laterallyone one side of said centerline at the locations at which the wallcurrents are circularly polarized when said waveguides are excited; e.each of said second broad walls having a plurality of pairs ofnonintersecting nonresonant slots, the two slots of each of said pairsof nonintersecting slots being orthogonal to each other and at an angleof 45* to the longitudinal centerline of said waveguides, the centers ofthe two slots of each of said pairs of nonintersecting slots beinglongitudinally separated from each other by substantially half a guidewavelength, said nonintersecting slots being disposed laterally on theopposite side of said centerline from said intersecting slots, each pairof said nonintersecting slots being centered longitudinally betweenpairs of intersecting slots, the ends of the two slots of each of saidpairs of nonintersecting slots that are proximate to said centerlinebeing farther apart than the ends that are distant therefrom; f. and theslot pattern of one of said waveguides being longitudinally displacedsubstantially half a guide wavelength with respect to the slot patternof the other of said waveguides.
 8. A circularly polarized planarantenna array comprising: a. a plurality of rectangular waveguides eachhaving first and second opposing broad walls, said waveguides beingparallel and adjacent And each being capable of supporting a travelingwave TE10 mode of propagation when excited; b. means coupled to saidwaveguides for feeding said waveguides with alternate ones thereof 180*out of phase; c. each of said first broad walls being corrugated todefine slow-wave structure providing substantially 25 percent reductionin guide wavelength; d. each of said second broad walls having aplurality of pairs of intersecting nonresonant slots, the two slots ofeach of said pairs of intersecting slots being substantially orthogonalto each other and at an angle of substantially 45* to the longitudinalcenterline of said waveguides, the centers of said pairs of intersectingslots being longitudinally separated from each other by substantiallyone guide wavelength, said intersecting slots being disposed laterallyon one side of said centerline at the locations at which the wallcurrents are circularly polarized when said waveguides are excited; e.each of said second broad walls having a plurality of pairs ofnonintersecting nonresonant slots, the two slots of each of said pairsof nonintersecting slots being orthogonal to each other and at an angleof 45* to the longitudinal centerline of said waveguides, the centers ofthe two slots of each of said pairs of nonintersecting slots beinglongitudinally separated from each other by substantially half a guidewavelength, said nonintersecting slots being disposed laterally on theopposite side of said centerline from said intersecting slots, each pairof said nonintersecting slots being centered longitudinally betweenpairs of intersecting slots, the ends of the two slots of each of saidpairs of nonintersecting slots that are proximate to said centerlinebeing farther apart than the ends that are distant therefrom; f. and theslot pattern of alternate ones of said waveguides being longitudinallydisplaced substantially half a guide wavelength with respect to the slotpattern of the other of said waveguides.
 9. A circularly polarizedantenna array comprising: a. means defining a waveguide having first andsecond opposing broad walls, said waveguide being capable of supportinga plurality of traveling wave TE10 modes of propagation along parallellongitudinal axes when excited; b. means coupled to said waveguide forfeeding said waveguide with waves which are 180* out of phase alongalternate ones of said axes; c. said first broad wall being corrugatedto define slow-wave structure providing substantially 25 percentreduction in guide wavelength; d. said second broad wall having aplurality of pairs of intersecting nonresonant slots and nonintersectingnonresonant slots disposed in longitudinal rows on alternate sides ofeach of said axes, the two slots of each of said pairs of intersectingslots being substantially orthogonal to each other and at an angle ofsubstantially 45* to said axes, the centers of said pairs ofintersecting slots being longitudinally separated from each other bysubstantially one guide wavelength, said intersecting slots beingdisposed laterally from said axes at the locations at which the wallcurrents are circularly polarized when said waveguide is excited; e. thetwo slots of each of said pairs of nonintersecting slots beingorthogonal to each other and at an angle of substantially 45* to saidaxes, the centers of the two slots of each of said pairs ofnonintersecting slots being longitudinally separated from each other bysubstantially half a guide wavelength, said nonintersecting slots beingdisposed laterally from said axes the same distance as said intersectingslots, each pair of said nonintersecting slots being centeredlongitudinally between pairs of intersecting slots, the ends of the twoslots of each of said pairs of nonintersecting slots that are proximateto one of said axes being farther apart than the ends that are distanttherefrom; f. anD the slot pattern along alternate ones of said axesbeing longitudinally displaced substantially half a guide wavelengthwith respect to the slot pattern along the other of said axes.
 10. Acircularly polarized antenna array comprising: a. means defining awaveguide having a broad wall, said waveguide being capable ofsupporting a plurality of traveling wave TE10 modes of propagation alongparallel longitudinal axes when excited; b. means coupled to saidwaveguide for feeding said waveguide with waves which are 180* out ofphase along alternate ones of said axes; c. said waveguide includingmeans defining slow-wave structure providing a reduction in guidewavelength; d. said broad wall having a plurality of nonresonant slotsarranged in longitudinal rows parallel to said axes, a row ofintersecting pairs of slots being on one side of each of said axes and arow of nonintersecting pairs of slots being on the other side of each ofsaid axes, the two slots of each of said pairs of slots beingsubstantially orthogonal to each other and at an angle of substantially45* to said axes, the centers of said pairs of intersecting slots beinglongitudinally separated from each other by substantially one guidewavelength, said intersecting slots being disposed laterally from saidaxes at the locations at which the wall currents are circularlypolarized when said waveguide is excited, the centers of the two slotsof each of said pairs of nonintersecting slots being longitudinallyseparated from each other by substantially half a guide wavelength, saidnonintersecting slots being disposed laterally from said axes the samedistance as said intersecting slots, each pair of said nonintersectingslots being centered longitudinally between pairs of intersecting slotson the opposite side of the proximate one of said axes, the ends of thetwo slots of each of said pairs of nonintersecting slots that areproximate to one of said axes being farther apart than the ends that aredistant therefrom; e. and the slot pattern along alternate ones of saidaxes being longitudinally displaced substantially half a guidewavelength with respect to the slot pattern along the other of saidaxes.
 11. A circularly polarized antenna array comprising: a. meansdefining a waveguide having a broad wall, said waveguide being capableof supporting a plurality of traveling wave TE10 modes of propagationalong parallel longitudinal axes when excited; b. a plurality of modesuppressors disposed in said waveguide for suppressing modes ofpropagation other than said plurality of TE10 modes; c. means coupled tosaid waveguide for feeding said waveguide with waves which are 180* outof phase along alternate ones of said axes; d. said waveguide includingmeans defining slow-wave structure providing a reduction in guidewavelength; e. said broad wall having a plurality of nonresonant slotsarranged in pairs staggered across said axes at substantially half aguide wavelength spacing intersecting pairs of slots being on one sideof each of said axes and nonintersecting pairs of slots being on theother side of each of said axes, the two slots of each of said pairs ofslots being substantially orthogonal to each other and at an angle ofsubstantially 45* to said axes, the centers of said pairs ofintersecting slots being longitudinally separated from each other bysubstantially one guide wavelength, said intersecting slots beingdisposed laterally from said axes at the locations at which the wallcurrents are circularly polarized when said waveguide is excited, thecenters of the two slots of each of said pairs of nonintersecting sslots being longitudinally separated from each other by substantiallyhalf a guide wavelength, said nonintersecting slots being disposedlaterally from said axes the same distance as said intersecting slots,each pair of said nonintersecting slots being centered longitudInallybetween pairs of intersecting slots on the opposite side of theproximate one of said axes, the ends of the two slots of each of saidpairs of nonintersecting slots that are proximate to one of said axesbeing farther apart than the ends that are distant therefrom; f. and theslot pattern along alternate ones of said axes being longitudinallydisplaced substantially half a guide wavelength with respect to the slotpattern along the other of said axes.